PROJECT SUMMARY Toxoplasma gondii is an obligate intracellular parasite with the ability to infect virtually any nucleated cell from any mammalian or avian species. Most infections in humans are asymptomatic but as to evade the immune response the parasite converts to an encysted form, thus establishing a chronic infection. These cysts, which mostly form in neural and muscular tissues, are not static latent structures and parasites continue to divide within the cyst wall and cysts can rupture releasing parasites that go on to invade other cells. Thus, an inflammatory response is likely present during chronic Toxoplasma infection, which has been confirmed in the brain of infected mice. Whether chronic or intermittent inflammation and ensuing pathogenesis occurs in other organs during a Toxoplasma infection has not been fully explored. Of particular interest is the prostate, in which inflammation is associated with benign prostatic hyperplasia (BPH) and prostate cancer. We have recently discovered that both tachyzoites and bradyzoites are present in the prostate of infected mice. Importantly, Toxoplasma infection in mice results in chronic prostate inflammation lasting beyond 60 days. Remarkably, infected prostates exhibit severe reactive hyperplasia and a histological pattern of ?microglandular? hyperplasia, two pathological features of human BPH not normally observed in murine models of prostate inflammation. Thus, it is our overall hypothesis that Toxoplasma infection contributes to prostate pathogenesis in humans. Pilot experiments indicate that markers of Toxoplasma infection are present in human BPH specimens and that men seropositive for Toxoplasma are more likely to have an elevated prostate serum antigen (PSA), a marker of prostate inflammation, than seronegative individuals. These preliminary results provide strong rationale to investigate a possible co-relation between Toxoplasma and prostatic disease. Accordingly, we will perform a retrospective analysis of serum, cDNA and tissue from men with symptomatic BPH compared to non- diseased men, correlating Toxoplasma exposure with inflammation, hyperplasia, cytokine and growth factor expression. Additionally, we will use our mouse infection model to study the mechanisms of Toxoplasma's propagation and pathogenesis in the prostate. Specifically, we will test whether Toxoplasma can infect the prostate through a natural infectious route, whether the parasite persists in the prostate as either a chronic or acute infection, and whether the effects of infection are global or constrained to invaded cells. Finally, we will perform transcriptomic analysis of infected prostate cells to determine the molecular effects of infection in these particular cells. By focusing on an unexplored aspect of Toxoplasma infection, the proposed work will reveal novel mechanistic information about Toxoplasma's interaction with its host and potentially uncover a possible connection between one of the most common parasites of humans and prostate disease.